Pope Francis reiterated Saturday that abortion is unacceptable, saying its use amounted to the hiring of a "paid killer."

"Is it lawful to eliminate a human lift to resolve a problem? It is lawful to hire a paid killer to resolve a problem," Francis asked during a conference at the Vatican on the use of abortion when the unborn child is found to have a serious illness.

"No human being can ever be incompatible with life," he said, adding: "Every child is a gift that changes the history of a family... and this child needs to be welcomed, loved and cared for."

In cases where the child may not live for very long, medical care is not wasted but by gaining time, allows parents to prepare for the death.

"That child will remain in their lives forever," he said.

Pope Francis used similar "paid killer" remarks in relation to abortion in October 2018, sparking a sharp reaction in medical circles.